In order to effect ion nitriding (or other forms of ion reaction) a plasma must be generated within a vacuum chamber. As is well understood a plasma phenomenon can be effected by providing a difference of potential across an ionizable gas such as nitrogen. In the prior art the difference of potential has been created between the hearth and the wall of the furnace chamber by connecting the wall of the chamber to ground and connecting the hearth to a negative potential. In such arrangements the hearth is independently connected by a power feed through device to a power source. The present system eliminates the need for independent power feed through devices. As is well understood, an ion nitride surface is partially effected by a reaction between ions of nitrogen along with ions of hydrogen and the workpiece. Ion nitriding is often desirable to provide a hard surface for a piece of equipment. For instance an ion nitrided surface is developed on gears which need to be surface hardened. Such a reaction is greatly influenced by the amount of heat present in the workpiece. In the prior art there has been difficulty in trying to directly monitor the temperature (and therefore the heat present) of the workpiece. Directly monitoring the temperature of the workpiece provides a basis for repeated successes in ion nitriding efforts. The present arrangement, because of the location of the thermocouple in each of the hollow supports, permits the temperature of the hearth and therefore the temperature of the workpieces to be continually and directly monitored which is an improvement over the prior art.